You can watch the launch here at Space.com, courtesy of ULA, or directly via the company.

ULA had originally targeted early December for NROL-71's liftoff, but bad weather and technical issues pushed the launch back multiple times. The most recent attempt, on Dec. 19, was nixed because of a slight hydrogen leak on the Delta IV Heavy — an issue that has taken several weeks to resolve.

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"We continue to remedy the technical issues that caused the last scrub of the Delta IV Heavy, and are working with our partners, the National Reconnaissance Office [NRO] and the U.S. Air Force, to ensure that we fly when it is safe to do so," Gary Wentz, ULA's vice president of government and commercial programs, said in a statement on Jan. 5. "We understand that this is a high-priority mission for the nation's war fighters, and we take our commitment to safety and mission assurance seriously."

NROL-71 will be operated by the NRO, which manages the United States' fleet of spy satellites. The activities of such spacecraft are generally classified, and NROL-71 is no different. Government officials have not disclosed details about the satellite's mission, and ULA is expected to end its launch webcast about 6 minutes after liftoff to help preserve secrecy.